Negative resist or dry develop process for forming middle of line implant layer

Abstract

A method of implanting a middle of line (MOL) implant layer of a flash memory device that does not require a descumming step is disclosed. In a first embodiment, the method includes depositing a negative tone resist over the MOL implant layer. Portions of the negative tone resist in and above a plurality of trenches are not exposed to optical radiation, while portions surrounding the plurality of trenches are exposed. The unexposed portions are developed out thereby leaving a bottom surface of each trench substantially free of a resist residue. Implants can be placed in the MOL implant layer without the need for a descumming step. In a second embodiment, a bi-layer resist is deposited on the MOL implant layer, wherein the bi-layer resist includes a silicon containing top layer and a bottom layer. The bi-layer resist is patterned to expose a portion of the bottom layer that resides in and above a plurality of trenches. The bottom layer is dry etch developed using oxygen plasma as the etchant, thereby leaving a bottom surface of each trench substantially free of a resist residue. Implants can be placed in the MOL implant layer without the need for a descumming step.